I. Field of the Invention
The present invention relates generally to automatic switching apparatus and, more particularly, to automatic switching apparatus for use with appliances having electronic controls.
II. Description of the Prior Art
The possibility of leaving an electrically operated appliance, such as a pressing iron, turned on and unattended for an extended period of time is a concern to many users. Some top-of-the-line pressing irons now provide the feature of automatic shut-off if the iron is not used for a predetermined period of time. Typically, the feature is included in a complete electronic control system using a microprocessor and an electromagnetic relay or a solid state switch such as a triac to control power to the heating element. Both of these devices are expensive and have other drawbacks as well. A triac, for example, requires a sizeable heat sink to dissipate its power loss when the iron is on and an iron is obviously a poor location for such a device because of the hot environment it represents. A power relay requires a significant amount of power to operate and tends to heat up when it is kept energized in the hot iron environment. Examples of prior art switching apparatus of the general nature just described include a pair of commonly assigned patent applications, namely, Ser. No. 687,842, filed Dec. 31, 1984, of Harry Albinger and Michael J. Marchetti for "Switching Apparatus for an Appliance Control Circuit" and Ser. No. 687,343, filed Dec. 31, 1984, of Thomas M. O'Loughlin for "Indicating and Control Apparatus for an Appliance".